President Donald Trump is in "excellent health," and has no cognitive problems, but should lose some weight through a regimen that includes improving his diet and getting more exercise, the White House physician said Tuesday.

"Absolutely, he's fit for duty, I think he will remain fit for duty for the remainder of his term," said Dr. Ronny Jackson, who oversaw Trump's first annual physical exam as president last Friday.

"The president's overall health is excellent."

"There's no indication whatsoever that he has any cognitive issues," Jackson told reporters at a White House news briefing.

"I find no reason whatsoever to think that the president has any issues whatever with his thought process."

Trump himself asked for an evaluation of his cognitive state, after questions were recently raised about it by a new book about the president, "Fire and Fury," said Jackson, who is a rear admiral in the U.S. Navy.

"He asked me to do it," Jackson said of Trump, 71, who last year became the oldest person ever to become president.

"The president has acknowledged he'd be healthier if he lost a few pounds," Jackson said.

To do that, the doctor said, he was looking to have Trump reduce his intake of fats and carbohydrates in his diet, and increase his physical exercise.

"He's more enthusiastic about the diet part than the exercise part," Jackson said.

Trump has a well-known penchant for fast food, including meals featuring McDonald's Big Macs and Filet-o-Fish sandwiches, and an aversion to exercise other than playing golf while using a cart to get around the links.

Asked how Trump managed to be in such good health with that lifestyle, Jackson said, "He has incredibly good genes."

Trump also has benefited from abstaining from both tobacco and alcohol throughout his life, according to the doctor.

Jackson said that while Trump "doesn't have a daily exercise regiment," Trump "has a lot of energy, a lot of stamina."

The doctor also mentioned that in addition to taking Advil and Crestor, a drug used to control cholesterol levels, Trump also takes Propecia, a drug used to stem hair loss.

"The president does take Ambien [a sleep aid] ... on overseas travel," Jackson said.

Jackson said a recent incident in which Trump slurred some words while making public remarks may have been the result of Sudafed that the doctor gave the president the previous day.

The briefing on Trump's physical by Jackson lasted almost an hour.

Jackson told reporters that the president personally asked that he answer every question put to him by reporters, and that press secretary Sarah Sanders was told by Trump not to interrupt the doctor during the briefing.